This invention relates generally to downhole pumps for extracting subterranean production fluids, such as crude oil, water or the like. More specifically, the invention relates to a downhole pump having a submersible downhole reciprocating pump member which is driven alternately up and down under fluid pressures generated by a surface located actuator and by gravitational forces, respectively. Through such reciprocation, the pumping member draws production fluid from the well during each upstroke and pumps such fluid toward the surface with each downstroke.
It is a common site across this country's oil fields to see so-called "walking beam pumps" slowly rocking up and down to extract oil from beneath the ground. According to conventional practice, these walking beam pumps employ lengthy jointed rods, known as sucker rods, for connecting the pump plunger in the well with the walking beam or pumping jack at the surface. In many instances these sucker rods may be hundreds or thousands of feet long. It is therefore not surprising that the initial costs and maintenance costs of walking beam systems are quite high.
There have been attempts at overcoming the shortcomings of walking beam pumps but those attempts have been largely unsuccessful. One attempt has been to position a downhole pumping device at the bottom of the well and to place an impacting device at the top of the well. The downhole pumping device usually includes a plunger which is biased upward by spring mechanisms and has a passage formed axially therethrough with a one way check valve located in the passage. The impacting device is repeatedly energized, causing sonic impulses to travel down the well hole to strike the plunger. Theoretically, each time the sonic impulse strikes the plunger it moves the plunger downwardly against spring bias, and the check valve opens to admit the fluid being pumped into the passage. Each subsequent spring biased upstroke of the plunger closes the check valve and causes a general upward movement of the liquid column with the uppermost portion thereof discharging through a delivery port.
While interesting in theory, the prior art sonic impulse pumping systems have not proven to be generally effective and reliable. Hence, oil production companies to this day still rely upon walking beam pumping technology.
It is therefore an object of this invention to overcome the shortcomings and expense of walking beam pumps. It is another object of the invention to advantageously utilize gravitational forces in pumping subterranean production fluids. Yet another object of the invention is to provide a pumping system which uses comparatively inexpensive and maintenance free components, particularly in the downhole components where routine access, inspection and maintenance is difficult to effect.
Therefore, to fulfill these and other objectives, as will become apparent from a reading of the following specification, the invention provides a downhole pump for pumping a production fluid from a well hole. The invention comprises a collection means communicating with the well hole for receiving the production fluid as it is pumped. A downhole pumping means is disposed within the well hole for generally vertical reciprocation therein and operable upon such reciprocation, to draw the production fluid from the well on each upstroke thereof, and to pump or expel the production fluid upwardly toward the collection means on each downstroke thereof. The invention further comprises an actuating means for causing the reciprocation of the pumping means comprising a gravitational means for urging the pumping means in the downstroke direction and a fluid pressure means for urging the pumping means in the upstroke direction.
Further, in accordance with the invention, the actuating means comprises an actuating cylinder and a piston reciprocable within the cylinder. The piston defines within the cylinder a first fluid chamber and a second fluid chamber, the second chamber being coupled to communicate with the well hole and to receive the production fluid. A supply of hydraulic fluid, maintained separate from the production fluid is at least partially contained within the first fluid chamber. A pressure generating means communicates with the first fluid chamber for cyclically altering the pressure of the hydraulic fluid within the first fluid chamber between a high pressure state and a low pressure state. The piston is responsive to the high and low pressure states within the first chamber to subject the production fluid within the well to corresponding high and low pressure states. The pumping means is responsive to the high pressure state of the production fluid within the well to overcome gravitational forces and thereby effect the upstroke or fluid drawing stroke. The pumping means is permitted, during each subsequent low pressure state to effect the downstroke or pumping stroke in response to gravitational forces.
Thus, it will be seen that the present invention uses gravity to pump production fluids up to the surface of the ground, and uses hydrostatic pressures, generated at the surface, to raise the reciprocating pump, thereby drawing a charge of fluid from the well for the next pumping cycle. The invention provides a marked improvement in pumping efficiency through this advantageous use of gravitational forces. Moreover, the downhole pumping mechanism is virtually foolproof with no springs to wear out and replace. Also, the above surface actuator uses a supply of hydraulic fluid which is contained completely separate from the production fluid being pumped. As production fluids, such as crude oil, are often laden with mineral deposits, dirt and sludge, the invention's use of a separate clean hydraulic fluid contributes to overall efficiency and low maintenance, and permits the use of lower horse power, commercially available and inexpensive pressure pumps.